1. Field of the Invention
This invention relates to the production of fiber composition acoustical tiles and panels for ceiling and wall decoration. More particularly, this invention relates to an apparatus and improved method for making acoustical products with highly discrete, finely detailed and sharply delineated three-dimensional patterns in the face of the panel.
2. The Prior Art
One way to form three dimensional patterns, holes and fissures in such panels is to cast a viscous aqueous pulp of fiber composition into a mold, pan or tray and press the surface with a screeding bar or blade, or solid embossing roller as described in U.S. Pat. Nos. 3,246,063 and 1,769,519. More particularly, according to these processes viscous aqueous pulps having a paste consistency similar to that of wet oatmeal are formed of a mixture of granulated mineral wool; a binder, particularly one of an amylaceous nature such as a thick boiling starch; fillers; coloring materials as needed and the like; and mixed with water to about 60-80% solids consistency. Various other materials may be added to give certain additional properties to the finished panel. This pulp is poured onto suitable trays which have been previously covered with a paper or metal foil liner to keep the composition from falling through perforations in the tray; and the trays, on a conveyor line, pass under an oscillating screed bar which tears the wet surface of the composition to form the patterned surface. The action of the bar rips or tears chunks of the granulated mineral fiber and other materials from the wet surface by friction as it passes under the bar. Frequently, it is difficult to adjust the speed of the conveyor line to the speed of the oscillating bar so as to maintain any pattern uniformity; and generally only shallow irregular patterns result.
In using an embossing roll to form such patterns, a solid cylinder is covered with a rubber matrix facing that has been engraved in a desired pattern. As the trays of pasty pulp, moving on the conveyor line, pass under the roll they cause the roll to turn and the pressure of the roll displaces a portion of the pulp under the "hills" portion of the patterned matrix to impress a "valley" design into the viscous aqueous pulp. Due partly to the resiliency and starchiness of the wet pulp, after being compressed within the cavities of the design, the pulp has a great tendency to bounce back towards its original shape upon release of pressure. Thus the patterns produced in this manner are characterized in being rather shallow and "mushy", lacking in fidelity by mushrooming around the detail of the pattern.
In both of these means the rough surface resulting may form the final pattern for the panel. Alternately the surface, after drying and curing of the panel may be sanded or planed to smooth off and flatten the "hills" of the patterns so that only "valleys" remain in a smooth-faced pattern.
Another way to form such panels involves first forming a consolidated water-felted fibrous mat in a continuous process by dewatering a very dilute fiber slurry. During dewatering the consistency of the slurry varies progressively from that of a dilute suspension to a thick fiber slurry or slush in which the fibers are still mobile in response to a moving force and finally to a wet felt in which the fibers are relatively fixed in position in a wet mat. At this latter stage the mat is usually compressed to a desired density for drying; and at that point a screeding bar or a rotating roll may be applied to the surface to produce fissures resembling natural marble or travertine stone. U.S. Pat. No. 4,226,674 discloses a rough texturing of the surface in such a process by making adjustments to the rotary vacuum cylinder picking up the slurry before mat formation and forming a roughly textured surface as the slurry is deposited on the forming screen before consolidating and draining to form a mat.